The vertebrae in a patient's spinal column are linked to one another by the disc and the facet joints, which control movement of the vertebrae relative to one another. Each vertebra has a pair of articulating surfaces located on the left side, and a pair of articulating surfaces located on the right side, and each pair includes a superior articular surface, which faces upward, and an inferior articular surface, which faces downward. Together the superior and inferior articular surfaces of adjacent vertebra form a facet joint. Each joint is surrounded by a capsule of connective tissue and produces a fluid to nourish and lubricate the joint. The joint surfaces are coated with cartilage allowing the joints to move or articulate relative to one another.
Diseased, degenerated, or otherwise impaired facet joints and/or discs can be surgically removed and prosthetic discs and/or facet joints implanted to restore natural function of a spine. Similar surgery may also be required after a laminectomy (removal of lamina), since a laminectomy predisposes the patient to instability and may lead to post-laminectomy kyphosis (abnormal forward curvature of the spine), pain, and neurological dysfunction.
However, implantation of an artificial facet joint frequently requires removal of a significant portion of the posterior ligamentous structures of the spine. This results in incomplete restoration of natural function of a spine as well as decreased stability and increased mobility (increased range of motion) of the patient's spinal column. Accordingly, there is a need for an artificial facet joint that would restore the natural function of a spine, including that of posterior ligaments.